The detection of gravitational waves by LIGO/Virgo and the success of LISAPathfinder have considerably modified the landscape of gravitational wave detection. This presentation will focus on the physics of GW which can be studied from space by LISA. After a description of the physics program that will be addressed by LISA, I will present the LISA detection scheme and the results obtained by LISA Pathfinder, explaining how this opens the way for spaced based detection. I will insist on the remarkable quality of the results obtained by LISA Pathfinder, many of which are beyond the expectations. I will conclude the presentation by giving an overview of the scheduling of LISA and an overview of the (present) French implication in this mission.